LCL型并网逆变器引发高频谐振是造成并网系统失稳最严重的原因之一,对系统的可靠运行造成了巨大的威胁。传统的基于逆变器自身端口阻抗重塑的有源阻尼方法不具备通用性,同时加大了控制环路的复杂程度,不利于用作多电力电子设备并网系统...LCL型并网逆变器引发高频谐振是造成并网系统失稳最严重的原因之一,对系统的可靠运行造成了巨大的威胁。传统的基于逆变器自身端口阻抗重塑的有源阻尼方法不具备通用性,同时加大了控制环路的复杂程度,不利于用作多电力电子设备并网系统的谐振抑制。关注到有源电力滤波器(active power filter,APF)动态控制环节的特点,基于无源性理论分析了APF用作阻尼输出的可行性及优势,提出了对APF进行模态切换以实现高频谐振的阻尼控制策略。该方案对谐振频率具备良好的跟踪效果,能够准确地识别系统模态并使APF迅速动作于对应频段的有源阻尼模态切换,具有通用性强、可靠性高、实现成本低的特点。通过仿真平台PLECS对提出的APF模态切换及高频谐振镇定策略进行验证,其结果与理论分析相符,进一步印证了APF用作有源阻尼抑制谐振的有效性。展开更多
An alternative technique for crack detection in a Timoshenko beam based on the first anti-resonant frequency is presented in this paper. Unlike the natural frequency, the anti-resonant frequency is a local parameter r...An alternative technique for crack detection in a Timoshenko beam based on the first anti-resonant frequency is presented in this paper. Unlike the natural frequency, the anti-resonant frequency is a local parameter rather than a global parameter of structures, thus the proposed technique can be used to locate the structural defects. An impedance analysis of a cracked beam stimulated by a harmonic force based on the Timoshenko beam formulation is investigated. In order to characterize the local discontinuity due to cracks, a rotational spring model based on fracture mechanics is proposed to model the crack. Subsequently, the proposed method is verified by a numerical example of a simply-supported beam with a crack. The effect of the crack size on the anti-resonant frequency is investigated. The position of the crack of the simply-supported beam is also determined by the anti-resonance technique. The proposed technique is further applied to the ＂contaminated＂ anti-resonant frequency to detect crack damage, which is obtained by adding 1-3% noise to the calculated data. It is found that the proposed technique is effective and free from the environment noise. Finally, an experimental study is performed, which further verifies the validity of the proposed crack identification technique.展开更多
The multi-crack damages modal of simple supported beam has been build, at the vibrating status, the multi-damage detecting method of simple supported beam measured by fiber Bragg grating strain sensing array has been ...The multi-crack damages modal of simple supported beam has been build, at the vibrating status, the multi-damage detecting method of simple supported beam measured by fiber Bragg grating strain sensing array has been studied. From 0 hz to 200 hz, using exciter vibrating simple supported beam, with different damages, resonant frequency of simple supported beam has changed. So, when the damage appears in simple supported beam, the local rigidity will decrease, the resonant frequency of simple supported beam will be affected, the damage status of simple supported beam have been determined by this. The experimental result indicates that the resonant frequency of simple supported beam has changed when there is no damage, one damage, two damages, three damages on simple supported beam. According to this, the fiber Bragg grating strain sensing array can detect multi-crack damage of simple supported beam under vibrating status.展开更多
文摘LCL型并网逆变器引发高频谐振是造成并网系统失稳最严重的原因之一,对系统的可靠运行造成了巨大的威胁。传统的基于逆变器自身端口阻抗重塑的有源阻尼方法不具备通用性,同时加大了控制环路的复杂程度,不利于用作多电力电子设备并网系统的谐振抑制。关注到有源电力滤波器(active power filter,APF)动态控制环节的特点,基于无源性理论分析了APF用作阻尼输出的可行性及优势,提出了对APF进行模态切换以实现高频谐振的阻尼控制策略。该方案对谐振频率具备良好的跟踪效果,能够准确地识别系统模态并使APF迅速动作于对应频段的有源阻尼模态切换,具有通用性强、可靠性高、实现成本低的特点。通过仿真平台PLECS对提出的APF模态切换及高频谐振镇定策略进行验证,其结果与理论分析相符,进一步印证了APF用作有源阻尼抑制谐振的有效性。
基金Project supported by the National Natural Science Foundation of China(No.50608036)Program for New Century Excellent Talents in Universities.
文摘An alternative technique for crack detection in a Timoshenko beam based on the first anti-resonant frequency is presented in this paper. Unlike the natural frequency, the anti-resonant frequency is a local parameter rather than a global parameter of structures, thus the proposed technique can be used to locate the structural defects. An impedance analysis of a cracked beam stimulated by a harmonic force based on the Timoshenko beam formulation is investigated. In order to characterize the local discontinuity due to cracks, a rotational spring model based on fracture mechanics is proposed to model the crack. Subsequently, the proposed method is verified by a numerical example of a simply-supported beam with a crack. The effect of the crack size on the anti-resonant frequency is investigated. The position of the crack of the simply-supported beam is also determined by the anti-resonance technique. The proposed technique is further applied to the ＂contaminated＂ anti-resonant frequency to detect crack damage, which is obtained by adding 1-3% noise to the calculated data. It is found that the proposed technique is effective and free from the environment noise. Finally, an experimental study is performed, which further verifies the validity of the proposed crack identification technique.
文摘The multi-crack damages modal of simple supported beam has been build, at the vibrating status, the multi-damage detecting method of simple supported beam measured by fiber Bragg grating strain sensing array has been studied. From 0 hz to 200 hz, using exciter vibrating simple supported beam, with different damages, resonant frequency of simple supported beam has changed. So, when the damage appears in simple supported beam, the local rigidity will decrease, the resonant frequency of simple supported beam will be affected, the damage status of simple supported beam have been determined by this. The experimental result indicates that the resonant frequency of simple supported beam has changed when there is no damage, one damage, two damages, three damages on simple supported beam. According to this, the fiber Bragg grating strain sensing array can detect multi-crack damage of simple supported beam under vibrating status.
